After 04.15 hours on 15 May 1941 the three masted Notre Dame du Châtelet was sunk by U-43 with 45 rounds from the deck gun and AA gunfire about 400 miles west of Ouessant. Lüth suspected the vessel to report the position of U-boats to Allied forces, while some of the survivors thought they had been attacked by a British submarine. The day before, the sailing vessel had encountered the Italian submarine Cappellini in 47°42N/13°56W. The ten survivors abandoned ship in three dories: Two men were picked up by the Italian submarine Otaria on 23 May, three men were rescued by the French fishing trawler Petite Bernadette off Belle-Île on 24 May and the remaining five men reached the Berlengas archipelago off Portugal on 28 May, after sailing approx. 600 miles in their dory.

The survivors reported that they were attacked without warning and that their dories were machine-gunned while they abandoned ship. More information about such incidents can be found in the following article: Treatment of Merchant Ship Survivors by U-boat Crews 1939 - 1945 written by Ken Dunn.